The invention relates to a device for monitoring the supply of printing liquid in the reservoir of an ink-operated printer or similar type of equipment, in which two electrodes, wetted by the printing liquid are employed in the monitoring operation.
In ink-operated printers of the type here involved, generally a printing head is moved by a motor, or other suitable means, along a data carrier, with the head being supplied with the printing liquid or ink through a supply line from an ink supply reservoir. While the ink reservoir may be made an integral part of the printer head, which has heretofore been proposed, visual monitoring of the ink supply in the reseavoir cannot be efficiently achieved in such a structure. However, a continuous monitoring of the ink supply is of great importance, particularly when printers of this type are employed in teleprinter and data printer applications.
Devices for determining the ink lever in an open vessel are known. For example, see IBM Technical Disclosure Bulletin Volume 16, No. 3, August 1973, page 775, in which device two electrodes are immersed in the liquid and, through an appropriate circuit arrangement, the capacitance between the electrodes is measured, with such capacitance changing in accordance with the level of the printing liquid. However, the dimensions of the ink supply reservoir impose restrictions on the capacitance, and as a result, the absolute magnitude of the capacitance change is extremely small. Consequently, a device of this type is relatively susceptible to disturbance through external influences, and the accuracy of the measurement can fluctuate considerably.